626 



MOLLUSCA 



PHYLUM VI 



Fig. 1160. 



Anaptychi. A, Amaltheus 

 spUialwf Brug. Lias. i/j. 

 B, Goniatites uchtensis Keys. 



some species from certain localities, inside the living chamber and close to the 



venter (Figs. 1159, 1161), a circumstance that led 

 Waagen to suppose they served to protect the nida- 

 mental gland of female shells. As shown by Michael 

 in Ojjpelia, even the embryonic shells were furnished 

 with aptychi.^ 



Aptychi are composed of three layers, of which the 

 middle one is the thickest and exhibits a cellular struc- 

 ture, whereas the two outer layers are comparatively 

 dense (Fig. 1164). Detached aptychi have been 

 classified by Zittel into several groups according to 

 their structure. Cellulosi (Fig. 1163) are smooth, thick 



plates, with punctate external surface; Imhricati (Fig. 1159) have the 



surface traversed 



by oblique folds 



or costae; Pundati 



(Fig. 1164, C) 



have rows of 



punctae and over- 

 lapping folds; 



Gramdosi include 



thin plates having 



the external sur- 

 face covered with 



concentric folds or 



rows of tubercles 



or spinules ; liiigosi 



are thick plates 



with irregularly 



arranged granules 



or rows of nodes 



Fic. 1161. 



Ifarpoceras lythense (Sowb.). 

 Boll, Wtirtemberg. Aptychus 

 chamber. 



Upper Lias ; 

 in the living 



Scaiihites spiniger Schltiter. 

 Upper Cretaceous ; Coesfeld, 

 Westphalia. Detached 



aptyclius. 



on the outer surface 



Nigrescentes (Fig. 1161) are covered 

 with a thin carbonaceous coat- 

 ing ; and Coalescentes (Fig. 1162) 

 have the two thin plates fused 

 along a median depression. This 

 last is a phylogerontic condition 

 of the aptychus occurring in 

 Sulphites. 



Classification. — Leopold von 

 Buch prepared the way for a 

 general classification of the 

 Ammonoidea by pointing out 

 three grand divisions which he 

 called "genera."' These were 

 the Paleozoic Goniatites, Ceratites, 

 from the Trias and Cretaceous, 

 and Ammonites, from the Jura 

 Von Buch's chief distinctions were based on the outlines of 



Fui. IKB. 



Aptychus laeris v. Meyer. Lithographic Stone ; Solenhofen, 

 Bavaria. ^1, External aspect; B, Internal. Vi- 



and Cretaceous. 



1 Michael, R., Zeitsclir. deiitscli. geol. Ges., 1894, vol. x]vi.—Retowski, 0., Neues Jahrli. Miii., 

 1891, vol. \\.—lilackmore. If. P., Geol. Mag., 1896, dec. 4, vol. iii. 



